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Occupational Safety and Health risks associated with the operation and maintenance of wind turbines

02 October 2014

Once operational, wind  farms are essentially unmanned facilities. Personnel access them only to perform maintenance and repairs. Unless they are involved in either planned or unplanned maintenance on a wind turbine, it is unusual for workers to be on site. This article is taken from the EU-OSHA European Risk Observatory Report ‘OSH in the wind energy sector’.

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During the construction phase, there could be more than 500 people working on site, but a typical operational crew will consist of two people for every 20 or 30 wind turbines in a wind farm. For smaller wind farms there may not be a dedicated operations and maintenance crew; instead, regular visits from regional teams are relied on. 

Once a tower is up and running, there are many maintenance procedures that must occur over the life of the structure. The typical routine maintenance time for a modern wind turbine is 40 hours a year (1). Maintenance issues have a link to design, particularly, as a typical installation may have a design life of 20 years, yet there are some parts of the installation, such as gear boxes, that may need to be repaired or replaced before then. Currently, gear boxes need to be replaced between 7 and 11 years into service (2). The more time a worker spends working on and maintaining a wind turbine, the greater the chance of his or her exposure to an OSH risk. In addition, owing to the shortage of skilled technicians in some EU countries, workers employed by some of the larger companies may be required to perform maintenance work in different countries, often working away from home for long periods.

Maintenance activities include common tasks such as cleaning blades, lubricating parts, full generator overhaul, replacing components and repairing electrical control units. These may be more repetitive tasks, which means that maintenance technicians become, in general, more familiar with the risks and the procedures in place for working at heights, interacting with electricity and working in confined spaces. Nonetheless, maintenance operations on wind turbines can be demanding and present a number of OSH hazards.

The types of challenges faced by workers carrying out maintenance on onshore and offshore wind farms are various and linked as much to the challenges associated with the installation itself as to external conditions linked to the environment and weather conditions, which can be extremely difficult, especially at sea.

Wind tower components with the higher failure rates will require more maintenance interventions. Extreme weather conditions such as snow, strong wind and rain can all result in temperatures that range from the very low to the very high, and these harsh conditions, together with dirt, dust and lightning, also contribute to the blades having to be repaired or cleaned regularly. For example, despite the hard composite nature of wind turbine blades, the leading edges eventually show wear that changes their aerodynamic properties to the point where power production drops significantly and maintenance work is needed.  The highest failure rates (3), in descending order, are:

·  electrical system;

·  rotor (i.e. blades and hub);

·  converter (i.e. electrical control, electronics, inverter);

·  generator;

·  hydraulics; and

·  gear box.

Interestingly, the industry tends to focus on gear box failures, because these cause wind turbines to be non-operational for the longest period of time. There is little in the literature about the risk of electrocution from working on or maintaining electrical components.

With regard to gear boxes, there has been some discussion about improving their reliability to reduce the instances of workers having to carry out maintenance, and newer turbine designs are opting for direct drive, which does away with gear boxes altogether (4). With regard to electrical risks, it appears that going over the nacelle may increase the risk of injury from sparking and electric shocks (which could lead to falls) or even electrocution, especially on some smaller, commercial-scale turbines that do not have brakes or shut-off mechanisms to prevent the turbine from accidentally being switched on during maintenance activities (see sidebar, ‘Good practice guide).

Electrical hazards from work being performed inside the turbine are a concern for both onshore and offshore facilities. These would include electrical arcs and electrical shocks that can cause electrical burns and electrocution. The presence of water in offshore wind farms may complicate certain operations such as cable laying and connecting (usually done remotely).

Maintenance work in, on or around the nacelle involves risks associated with moving parts should the nacelle turn, hot parts causing burns and high-voltage cables. If moving parts of the turbine (such as gears and blades) are not guarded properly they have the potential to cause severe injuries, such as crushed fingers or hands, amputations, burns or serious eye injuries that could lead to blindness.

Accessing the nacelle also means climbing very tall vertical ladders (e.g. 80m high) when there is either no lift in the wind turbine or the lift has failed. Workers may have to climb several times during a shift. This generates a high physical load on workers and may result in musculoskeletal disorders and physical  exhaustion. A certain degree of cardio-respiratory fitness and strength in the limbs is necessary. 

To conduct inspections and maintenance tasks associated with the blades, workers can use similar fall protection systems and equipment to those used for wind turbine installation. In certain cases where workers need to access to the blades from the outside, more specialised access equipment and rope access techniques should be implemented. In the case of frequent maintenance operations, permanent systems such as horizontal rail systems attached to the nacelle, or ground-mounted lifts to carry technicians up to a platform, can also be installed to provide fall protection. 

Fall  protection equipment for offshore workers is exposed to harsher elements, so it must be designed for extreme environmental  conditions. It should offer a high level of moisture ingress protection, with its components completely sealed inside the housing to prevent saltwater corrosion. Fall arrest equipment and harnesses should also be washed in fresh water more often  because excessive exposure to saltwater can damage equipment and put workers at risk (5).

Maintaining turbine blades will also involve operations such as buffing and resurfacing, which may expose workers to harmful gases, vapours and dusts (6). When inside the turbine, adequate ventilation should be provided to reduce inhalation hazards. If the ventilation alone is not adequate, then workers may also need to use appropriate respirators. Use of respirators may give a false sense of security and workers should understand the limitations of the respirators. For example, during heavy exertion the respirator seal is often compromised, which allows the hazardous substance to enter the breathing zone (without being filtered) through the gaps between the respirator and the wearer’s face. It is essential that workers are trained in the proper use of respirators, including storage and maintenance.

It is particularly important to monitor workers’ exposure to gases and dust during work in confined spaces (7). Throughout the wind turbine there are a number of areas that can be defined as confined  spaces, such as nacelles, blades, rotor hub, tower, tower basement and pad mount transformer vaults. Nacelles, blades, rotor hub, tower and tower basement have adequate size and configuration for worker entry but have limited means of access and egress and are not designed for continuous  worker occupancy.

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The United Kingdom industry guidance recommends that specific considerations should be given to working in these confined spaces, for example:

·  Oxygen depletion is always a concern when working in confined spaces. Toxic fumes can arisefrom heat or electrical sparks igniting solvent-based resins or other volatile organic compounds used to lubricate turbines, blades and electrical apparatus.

·  Workers who must crawl into the narrow, culvert-like spaces of a blade to inspect the wind turbine lighting or to repair the blades or fibreglass skin can be subject to off-gassing from battery acids or volatile organic compounds.

·  The decomposition of dead birds or rodents that may have found their way into the confined space may suck enough oxygen from the environment to cause unsafe oxygen levels.

·  Exposure to biologically generated compounds such as moulds.

Any maintenance technician entering a confined space should carry a portable gas monitor in his or her toolkit and must test air samples before entering the confined space, as these will warn against multiple threats posed by confined space entry, for example detecting toxic gases in parts per million levels and flammable gases at the lower explosive limit. A standard four-gas detector will include sensors for monitoring oxygen, hydrogen, carbon monoxide and hydrogen sulphide. These four gases deserve special attention in confined space work. For a permit-required confined space entry, that is when the confined space has the potential for hazards related to atmospheric conditions (toxic, flammable, asphyxiating) engulfment or any other recognised serious hazard, a written permit to enter must be issued by the employer. This permit will provide details on the steps that need to be taken to make the space safe before and during the entry. Training on how to deal with these risks and hazards within the confined space and the use of the measuring equipment is paramount for all maintenance workers. 

In addition to risks linked to hazardous substances and lack of oxygen in confined spaces, further issues such as ergonomics and musculoskeletal disorders linked to awkward, static postures need to be taken into consideration. Hot temperatures can also be an issue, for example when working within the nacelle, especially in summer, and this may also present a cardiovascular challenge.

Maintenance workers must also be able to manhandle a colleague in a confined space should the colleague suffer a health problem. Assisting with the rescue of an ill or injured colleague, or even only having to be prepared to act in the case such a situation may occur, is a factor of work-related stress.

As with the construction and operational phases, emergency response planning and rescue plans need to be in place. Workers should receive appropriate training in rescue procedures, which will involve practice evacuations from the nacelle, which could detail the necessary action in any type of emergency, including in the event of a suspension trauma when a worker is in a harness, which equipment should be used and the different evacuation methods and procedures. These will depend on the type of wind turbine and whether it is onshore or offshore.

In offshore wind farms, diving operations present some unique issues for operators, not only during installation but also during maintenance (8). Within the United Kingdom, there are a number of guidelines including the Diving at Work Regulations 1997 and an approved code of practice from the Health and Safety Executive (1998). Steps to manage risk include designing out diving operations and using remotely operated vehicles where possible; ensuring the selection of a suitable vessel, safe method of access and egress from vessels; ensuring diver competency; and management of diving operations to include recompression and emergency response planning (9).

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Maintenance workers, particularly those working offshore, may be subject to time pressures owing to the  availability  of  offshore  weather  windows,  and  this  could  militate  against  compliance  with  safe working practices (10).

In the United Kingdom, industry guidance recommends that planned preventative (11) maintenance should  take  place  during  the  summer  months,  when  weather  conditions  are  better,  and  that  such preventative maintenance contributes to avoiding the possibility of unplanned maintenance having to be carried out during the winter (12). In contrast, a dynamic maintenance plan has been suggested, with work being carried out as and when required, rather than on a preventative basis, and non-urgent tasks being delayed to spring or autumn when weather conditions may be less extreme . However, this type of plan is aimed more at improving reliability and costs than OSH.

From an OSH perspective, climbs should be limited to wind conditions less than 40 mph (64 km/h), and work should be scheduled for good weather. 

Scheduled maintenance is preferable to unplanned maintenance, which generally means poorer work organisation, and may involve workers who are not familiar with the wind farm/turbine to  be maintained ad hoc and the specific challenges associated with its location. If reactive maintenance is required, it is recommended (13) that consideration is given to weather working limits; the availability of sufficient light for operatives to work safely if night working is required; the availability of appropriate PPE depending on the tasks to be undertaken and location; and emergency procedures. Research is being carried out to further improve the online remote monitoring of equipment (14), which would reduce the need for unplanned maintenance.

To further reduce the need for maintenance and exposing workers to risk, it has been recommended that turbine subassemblies should be more thoroughly tested, particularly converters and generators, to eliminate early failures. Another suggestion is that nacelles should be tested at full or varying load, and at elevated temperatures to force early failures to occur, so that they enter service  with an improved reliability (15). This could apply equally to both onshore and offshore turbines. However, this does not take into account installations that go beyond their intended service life (16).

References

(1) IFC, 2007

(2) Puigcorbe and deBeaumont,  2010

(3) Spinato, 2009

(4) Puigcorbe and de-Beaumont, 2010; IFC, 2007, Professional Engineering, 2009

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(5) Global  Wind Organisation, 2012

(6) Aubrey, 2011).

(7) Galman, 2009

(8) Atkinson, 2010

(9) RenewableUK, 2010b, 2012

(10)Health and Safety Executive, 2010

(11) Planned preventative maintenance is where maintenance and inspections are scheduled at regular intervals to identify potential risks before they become problems.

(12) RenewableUK, 2010

(13)RenewableUK, 2010

(14) Professional Engineering, 2009

(15) Spinato, 2009

(16) Chartered Institute of Environmental Health, 2008

(17) Cenifer 2012


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